Flux guide and gate arrangements



June 28, 1955 C. E. ELLSWORTH FLUX GUIDE AND GATE ARRANGEMENTS Filed Dec. 27, 1951 4 Sheets-Sheet l I l V EN TOR.

CARL E. ELLSWORTH BY m n @m% ATTORNEYS June 28, 1955 c. E. ELLSWORTH 2,712,050

EUX GUIDE AND GATE ARRANGEMENTS Filed Dec. 27, 1951 4 Sheets-Sheet 2 Fig. 3

INVEN TOR.

CARL E. ELLSWOR-TH BY Mums! lnducifince ATTORNEYS June 28, 1955 c. E. ELLSWORTH 2,712,050

FLUX GUIDE AND GATE ARRANGEMENTS Filed Dec. 27, 1951 4 Sheets-Sheet 3 Fig. 4

INVENTOR.

BY CARL E. ELLSWORTH ATTORNEYS v June 28, 1955 c. E. ELLSWORTH FLUX GUIDE AND GATE ARRANGEMENTS 4 Sheets-Sheet 4 Filed Dec. 27, 1951 Fis.8

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INVENTOR Carl EEUsworEh BY w n 60% M W 15620.

ATTORNEY 9 sigumauts, to Plastic (Jyi' ndcr Gas Qompany, (Illicage, corporation of Delaware Application December 27, 1951, Serial No. 26,599

3 Claims. (Cl. 219-40155) This invention is concerned with improvements in reentrant tunnel devices especia ly suited for rapid dielectric heating of lar e-area loads such as foam-rubber mattresses, Ill-board panels, groups of sand cores or plastic prefoims, and the like.

'lhe high-freon :rcy heating appar tus disclosed herein the improvements her claimed form no of the present invention. Such high-frequency heatapparatus the numerous patentable features thereof form the subiect matter of copending applicaticns filed by the applicant, Henry R. Warren, and owned by the same assignee as the present application. More particularly, Serial No. 419,633, filed March 26, 1954,

t r Serial No. 138,628, filed January oses and claims features of the highfrequency heating apparatus including the circuitry and the ent nt cavity; applications Serial Nos. 419,070 and 4193371, both filed March 26, E954, are continuationsin-part of Serial No. 138,628 and are directed respectively to dnterent features of the fin structure; application Serial No. M91374, filed rch 26, i954, is a continuation-impart of said applic t'on Serial No. l3S,628

with claims directed to the coupling loop structure and cooling means therefor; and Serial No. 419,072, filed March 26, 1954, which is concerned with llux guide and gate arrangements including conductive plate structure disposed in operative relation with respect to the coupling loop modi the mutual inductance of the loop and the resonator. The disclosures of the aforesaid applications are to be taken prior art against the present application.

The present invention has been illustrated as applied to a resonant tunnel device or :eentrant resonator of the type disclosed and claimed in the aforesaid copending applications and comprises a metal-walled enclosure in which an inductance structure frequently referred to as fin eat is from one wall in spaced relation to the remaining walls to form the lumped inductance of a resonant circuit whose capacitance is principally formed by an electrode attached to the free end of the fin structure. For transfer of high-frequency power to or from the tunnel circu t a coupling loop of one or more turns is disposed within the tunnel space which encircles the fin structure.

In accordance with the present invention an auxiliary conductive plate structure is conductively attached to either or both sides of the coupling loop and operating at the potential of the loop effectively alters in the vicinity of the loop the concentration of the magnetic flux about the inductive structure or fin. The modifying conductive plate structure may, in whole or in part, be stationary to serve as a flux guide, or it may, in whole or in part, be movable to serve as a flux gate.

The invention further resides in features of construction, combination and arrangement hereinafter described and claimed.

For a more complete understanding of the invention and for illustration of various modifications thereof ref- Patented June 28:, 1955 2 erence is made to the accompanying drawings in which:

Fig. l is a top plan view, in part broken away, of a dielectric heating tunnel;

Fig. 2 is an elevational View in section taken on line 2-2 of Fig. 1;

Fig. 3 is an enlarged plan view of parts schematically shown in Fig. 1;

Fig. 4 is a side elevational view in section of parts shown in Fig. 3;

Fig. 5 is a perspective view of flux structure shown in Figs. 1 to 4;

Fig. 6 is a top plan view of a modification of the arrangement of 1;

Fig. 7 is a transverse sectional elevation view of the modification of Fig. 6 and schematically illustrates a tunnel oscillator circuit;

Figs. 8 and 9 are respectively a top plan view and a transverse sectional elevation view of another modification of the arrangement of Fig. l; and

Fig. 16 is an explanatory figure.

Referring to Figs. 1 and 2, a tunnel or reentrant resonator T is shown as an enclosure which may be formed of sheet metal, reinf rced when necessary by an external framework (not shown). A fin structure P which forms the lumped inductance of the resonant circuit of the tunnel may also be of sheet metal. In the particular form shown in Fig. l, the fin is a hollow box structure extending downwardly and inwardly from the top Wall of the tunnel. The upper edge of the fin is electrically and mechanically attached to the upper Wall; in the particular form shown in Figs. 1 to 5, such attachment is effected by a plurality of flexible strips 1d of metal or metal alloy having high conductivity such as an aluminum or copper alloy.

To the lower, free end of the fin F is attached a metal plate E serving as one plate of a capacitor whose other plate, in the particular structure shown in Figs. 1 and 2, is provided by the lower wall of the tunnel itself. However, as in the aforesaid Warren applications, the other electrode may be spaced from the lower wall of the tunnel and may be a conveyor. This interelectrode capacity forms most of the capacity of the resonant tunnel circuit. The length of the fin as measured between the electrode E and the upper wall of the tunnel is small compared to one wavelength at the operating frequency of the tunnel so that the fin current is substantially constant from one end of the fin to the other. The dimensions of the electrode E, particularly the distance to the rim as measured outwardly from the fin, is usually a small fraction of a wavelength at the operating frequency of the tunnel, so that the electrode E is a substantially unipotential surface: such distance may be a larger fraction in any one or more directions from the fin if a potential rise in such direction or directions is desired.

In operation of the tunnel or reentrant resonator, as also described in the aforesaid Warren applications, the space encircling the fin structure F is traversed by a high-frequency magnetic field. For transfer of highfrequency energy to or from the tunnel circuit, a coupling loop L is disposed within this space above the electrode E.

As also disclosed in aforesaid applications, the coupling loop L may be in the plate circuit of a high power oscillator tube whose resonant tank circuit is formed by the tunnel, in which case the coupling loop may be a wide band of copper fastened to the outside of a loop form provided by copper piping which serves to conduct cooling liquid for the oscillator tube. A suitable oscillator circuit is shown in Fig. 7 so that the purposes and advantages of the invention may be better understood. In brief, the anode of the tube V is connected to one terminal of the loop L whose other terminal is connected to the grounded wall structure of the tunnel. A directguide and gate current source of high voltage is connected between ground and the cathode of tube V; the positive terminal of that source being grounded as indicated. The grid of tube V is connected to the tunnel electrode B through adjustable capacitor C1. The capacitor C1 and the capacitor C2, in whole or in part provided by the effective input capacitance of tube V, provide a capacitive potential-divider which as also explained in the aforesaid Warren applications is utilized in automatic stabilization of the grid-voltage. A direct-current path between the grid and cathode of tube V is provided by radio-frequency choke RFC and grid-leak resistor R1.

As indicated in Fig. 10, and as also discussed in the aforesaid Warren applications, the mutual inductance of the anode loop and tunnel circuits should be supraoptimum to maintain the voltage of electrode E substantially constant despite changes in power factor of the load. Such changes occur due to changes with heating of the load and in the case of a conveyor-fed tunnel to varying number of load objects in the interelectrode space. The several curves of Fig. 16 show that when the mutual inductance is appreciably larger than the optimum value 0, a substantial change in power factor of the load with corresponding change in Q of the tunnel circuit produces a relatively small change in the electrode voltage, whereas with infra-optimum coupling, the electrode voltage changes very rapidly with change of power factor.

In the use of the tunnel T as an applicator, the dielectric load to be heated is disposed in the high-frequency field between the electrode E and the bottom wall of the tunnel. For adjustment of the potential gradient through the load or to apply pressure to the load, the electrode E is raised or lowered to suitable position, the flexible sections it? of the fin permitting such adjustment.

In accordance with the present invention, to obtain the desired supra-optimum mutual inductance of the anode loop and the tunnel or resonator circuits required for the optimum operating conditions for a particular use of a tunnel, an auxiliary conductive plate structure is supported on and carried by the coupling loop L. In the particular arrangement shown in Figs. 1 to 5, this plate structure comprises a stationary metal plate 11 suitably fastened to that side of the coupling loop which is the closer to the adjacent side wall of the tunnel. To

each end of the stationary plate 11 there is hinged a movable plate 12 which can be adjusted toward and away from the full-line position, Fig. 1, in which it is in direction normal to the fin and to the dotted line position in which it is parallel to the fin.

The area of each of the plates 12 is preferably somewhat greater than the cross sectional area of the coupling loop L. For adjustment of the plates 12, 12 which serve as flux gates, they are each attached as by an insulating link 13 to a shaft 14 extendin" through the upper wall of the tunnel. Both shafts may be mechanically coupled to an operating motor, not shown, operable from the control panel of the heating system to vary the mutual inductance and thus the voltage of the electrode and therefore the radio-frequency power applied to the load.

The upper portions of the flux gates 12 are cut away as indicated at 15 suitably to clear the flexible strips 16 of Figs. 1 to 5 throughout the range of lifting and lowering of the fin the attached electrode. The electrode lifting mechanism need not be described as it is not part of the present invention. The flux gates 12, 12 and guide plates 11 are of high-conductivity metal such as copper for example.

The stationary plate or flux guide 11 determines a limit of the range (Fig. 10) through which the mutual inductance of the coupling loop L and tunnel T is Variable by adjustment of the flux gate plates 12, 12. Such flux gates are particularly useful as a means for controlling the power to the load when the electrode E must rest upon the load as in the heating of wallboard.

When the tunnel is always to be used for heating of a type of load which does not require the electrode E to rest upon the load, the flux gates 12 may be omitted since power to the load may be controlled by varying the position of electrode E. In such case, as shown in Figs. 6 and 7, the auxiliary plate structure may consist simply of stationary plate 11 attached to and carried by the loop L and suitably extended to intersect or 'cut part of the magnetic field. The plate 11 is so dimensioned and positioned that there is obtained the desired mutual inductance between the resonant tunnel and the anodecircuit loop. Thus, similar tunnel and loop construe tions may be used for a wide variety of heating uses by addition to the loop of different flux guides each suited to obtain the mutual inductance required for a particular heating use. Such flux guide plates may be used to advantage in multi-tunnel systems in which foam-rubber mattresses, for example, are in turn conveyed through successive tunnels energized by their respective oscillators. The requirement of diferent electrode voltages at different stages of drying may readily be met by using oscillator and tunnel arrangements which are generally similar but which have suitably different flux guide plates. When attached to the hot side of the coupling loop, the plate 11, at the potential of the coupling loop, and flux gates 12, i2, may serve as one plate of a condenser effectively in shunt to the loop L and affecting the resonant frequency of the anode circuit.

What is claimed is:

i. In combination with a resonant high-frequency heating device comprising an applicator having conductive walls forming a part of a reentrant resonator, metallic inductance structure electrically connected at one end to one of said walls and projecting into the interior of said applicator to provide inductance for the resonator, a pair of high-frequency heating electrodes providing a space within said applicator for receiving work to be heated by an electric field between said electrodes, means supporting one of said electrodes at the inwardly projecting opposite end of said metallic structure in spaced relation to said walls to provide capacitance for said resonator, said one electrode being electrically connected through said structure to said one of said walls, said other electrode being electrically connected by way of said conductive walls to said one end of said metallic structure, and a coupling loop disposed in the resonator space which encircles said metallic structure for exciting the resonator to create an electromagnetic field whose lines of flux will encircle the tin structure and link with the coupling loop, the improvement which comprises means for modifying the mutual inductance of said loop and the resonator comprising conductive plate structure attached to and supported by said loop and operating at the same potential as said loop and extending from the boundaries of said loop to intersect said flux at regions external to said loop to alter the concentration of magnetic flux linked by said coupling loop.

2. The improvement in the resonant high-frequency heating device as in claim 1 in which at least a part of said extending conductive plate structure carried by said loop is movable variably to modify the mutual inductance of the loop and resonator.

3. In a resonant high-frequency heating device comprising conductive walls defining a reentrant resonator, metallic fin structure extending from a first of said walls and spaced from the other walls to provide inductance for the resonator, an electrode connected to the free end of said fin structure in spaced relation to the resonator wall opposite said first wall to provide capacitance for said resonator, and a coupling loop disposed in the resonator space which encircles said fin structure, the improvement which comprises conductive plate structure attached to and supported by said loop and operating at the same potential as said loop and disposed in said resonator space for modifying the mutual inductance of said loop and the resonator, said plate structure consisting in part of a stationary portion substantially parallel to the adjacent wall of the ti 1 structure and in part con, sisting of structure extending outwardly from the boundaries of said loop and movable relative to said loop and said fin structure, said movable structure variably intersecting said flux at regions external to said loop to alter the concentration of magnetic flux linked by said coupling loop.

Referenees Cited in the file of this patent UNITED STATES PATENTS Goldstine Sept. 24, Usselman et al Oct. 15, Curtis Mar. 2, Goldstine Feb. 29, Herold Nov. 5, Dakin et a1. Apr. 18,

inn Mar. 20, Mittelmann May 8, Baker et al. Apr. 28, 

